The prior art has employed various methods and apparatus for the molding of plastic materials and the like. Generally, all such molding can be classified into two categories, one of which comprises the molding of thermosetting materials and the other of which comprises the molding of thermoplastic materials.
Both of such categories of molding, however, have, heretofore, experienced difficulties. For example, in the molding of any desired article, it is of obvious benefit to be able to mold such article, as a finished product, and eliminate the necessity of having to in any way expend additional manpower on such articles, in what may be referred to as "corrective" operations, upon the removal of such articles from the associated mold cavity; however, with one expensive exception, the prior art failed to provide either a method or apparatus which would produce such articles.
The problems of the prior art may be better understood from reference to the mold cavity itself. That is, as is well known, the cavity of the mold is formed so as to conform to the desired configuration of the finished molded article. However, the volume of such cavity is often difficult to compute especially when one considers that the material to be introduced into such cavity often undergoes expansion when so introduced and heated (in the case of thermosetting plastics) or cooled (in the case of thermoplastic materials).
Therefore, generally, in an attempt to make sure that upon each molding cycle there is sufficient molding material to fill the mold cavity, the prior art has resorted to the use of sprue type gates whereby a substantial quantity of molding material is ultimately molded integrally with the molded article in the form of an extending sprue. Upon removal of such molded article from the associated mold cavity the extending sprue carried thereby has to be removed as by a subsequent cutting operation. Not only is such a cutting operation costly, in that it does not contribute anything directly to the molding of such articles, but the material contained in the cut-off sprue is almost always totally wasted.
In some instances, especially where material costs are high, the prior art has atempted to avoid the necessity of first forming sprues and subsequently cutting them off, by, for example, weighing the constituent comprising the moldable material. That is, through an extensive and costly procedure of trial and error, the precise volume of moldable material required to adequately fill the cavity and mold the article therewithin is determined. This quantity is, in effect, weighed and from then, by injection, that (theoretically) exact same quantitiy of moldable material is injected into the related mold cavity to form the resulting molded article without the presence of an attendant sprue. The preceding method of weighing constituents is also often followed in what is commonly referred to in the art as compression molding.
Accordingly, it can be seen that the prior art, in attempting to avoid the costs of sprue formations has, in effect, employed molding methods which are often substantially as costly as the actual removal of formed sprues.
The invention as herein disclosed and described is primarily directed to the solution of the above as well as other related problems.